Lifting mechanism

ABSTRACT

Apparatus for raising and lowering workmen and tools into proximity with elevated structures during construction and repair thereof comprises a platform, a frame and a hydraulicallyactuated linkage assembly connecting the platform to the frame. The linkage assembly comprises an elongated boom assembly pivotally connected to one end of the platform, a compression member assembly pivotally connected to one end of the frame and to the boom assembly, and a tension member assembly pivotally connecting the other end of the boom assembly to the frame. A main hydraulic actuator is connected between the compression member assembly and the frame and operates upon extension to pivot the compression member assembly in one direction to cause the tension member assembly to pivot the boom assembly in the other direction for raising the platform. Auxiliary hydraulic actuator means connects the boom assembly to the platform, and an automatic levelling system is provided to operate the auxiliary actuator means for maintaining the platform level during raising and lowering thereof.

United States Patent 119;

Beucher 1 1 LIFTING MECHANISM Robert A. Beucher, 216 Howarth Road, Media, Pa. 19063 [22] Filed: Dec. 7, 1973 [21] Appl. No.: 422,971

{76] Inventor:

Primary Examiner-Reinaldo P. Machado Attorney, Agent, or Firm-Howson & Howson [57] ABSTRACT Apparatus for raising and lowering workmen and tools 1 July 8,1975

into proximity with elevated structures during construction and repair thereof comprises a platform, a frame and a hydraulically-actuated linkage assembly connecting the platform to the frame. The linkage assembly comprises an elongated boom assembly pivotally connected to one end of the platform, a compression member assembly pivotally connected to one end of the frame and to the boom assembly, and a tension member assembly pivotally connecting the other end of the boom assembly to the frame. A main hydraulic actuator is connected between the compression member assembly and the frame and operates upon extension to pivot the compression member assembly in one direction to cause the tension member assembly to pivot the boom assembly in the other direction for raising the platform. Auxiliary hydraulic actuator means connects the boom assembly to the platform, and an automatic levelling system is provided to operate the auxiliary actuator means for maintaining the platform level during raising and lowering thereof.

14 Claims, 6 Drawing Figures SHEET F? E? 3 FIGS.

FIG5.

LIFTING MECHANISM The present invention relates to man-lifting apparatus, and more particularly, the present invention relates to apparatus for raising and lowering a platform designed to support workmen while working on elevated structures.

In the construction and maintenance of elevated structures, it is often necessary for workmen to be supported in close proximity with the structures. A socalled Cherry-Picker" type of lifting apparatus has found wide-spread use as in recent years since it is capable of omni-directional control by the workman supported therein. Although Cherry Picker apparatus is adapted to be utilized in a variety of environments, it is generally not designed to accommodate more than one workman at a time or to support a relatively large complement of tools and equipment. Thus, it is not particularly useful in servicing overhead electric cables, such as extend above railroad tracks, because such servicing requires a number of workmen to be able to walk back and forth along the cable while working. At present, some railroads have elevated platforms permanently mounted on railroad cars for supporting workmen at the proper elevation with respect to an overhead cable. Although this approach is satisfactory, it has the obvious disadvantage of typing-up a railroad car which could be used for other purposes. Moreover, when work is to be conducted at a particular track location, it is necessary for the car to be coupled to an engine and transported to the location. Hence, even when only a relative minor amount of work is to be performed, a considerable amount of equipment is required merely to provide a platform for workmen.

Trucks having retractable track-engaging wheels which enable the truck to travel along railroad tracks are presently used to transport railroad crews to various track locations. Such trucks have the advantage of being able to get on and off the tracks at railroad grade crossings, and although capable of transporting workmen and tools to a work site, heretofore they have not been equipped with means to elevate a platform to enable workmen to work on overhead cables. Accordingly, it should be apparent that such a vehicle equipped with lifting apparatus which is capable of being transported in a compact configuration and which is capable of being extended into an erect usage configuration to dispose a platform into proximity with overhead structures is highly desirable.

With the foregoing in mind, it is a primary object of the present invention to provide an improved manlifting device.

It is another object of the present invention to provide a novel mechanism for raising and lowering a work platform.

As a further object, the present invention provides a man-lifting device which is capable of being transported on a vehicle in a compact folded configuration and of being extended into an erect usage configuration at a work site.

It is a further object of the present invention to provide a simple linkage assembly for mounting a work platform to a mobile frame in such a manner as to permit the platform to be elevated steadily to a substantial level with respect to the frame and with a minimum of horizontal movement.

Yet another object of the present invention is to provide a safe but simple man-lifting structure.

These are other objects, features and advantages of the present invention should become apparent from the following description when taken in conjunction with the accompanying drawings in which:

FIG. 1 is a side elevational view of lifting apparatus embodying the present invention, the view illustrating in full lines the position of the apparatus in its extended usage configuration and illustrating in broken lines the position of the apparatus in its folded transportation configuration.

FIG. 2 is an enlarged side elevational view of the apparatus of FIG. 1, the view illustrating the position of the apparatus in an intermediate location;

FIG. 3 is a rear elevational view looking leftward along lines 33 in FIG. 2;

FIG. 4 is a fragmentary side elevational view of a modified embodiment of the present invention;

FIG. 5 is an inverted plan view taken along lines 5-5 of FIG. 4; and

FIG. 6 is a schematic diagram illustrating an hydraulic system for automatically maintaining the platform level during raising and lowering thereof.

Referring now to the drawings, there is illustrated in FIG. I lifting apparatus 10 embodying the present invention. As best seen therein, the apparatus 10 is mounted on a truck 11 of the type which mounts retractable railroad wheels 12 and 13 to enable the truck 11 to travel either on a road or on railroad tracks when the wheels 12 and 13 are extended. The truck 11 has a chassis formed by a pair of rearwardly-extending chassis members 14a and 14b, and the lifting apparatus 10 is mounted on the chassis members 14a and 14b.

The lifting apparatus 10 is capable of being transported in a compact configuration, illustrated in broken lines in FIG. 1, and the apparatus 10 is capable of being expanded into an erect usage configuration, illustrated in full lines therein. To this end, the apparatus 10 comprises a frame 15 having a pair of horizontallydisposed parallel frame members 15a and 15b (FIG. 3) which are secured onto the top sides of the chassis members 14a and 14b, and which are tied together front and rear by braces 16 and 17, respectively. A platform 20 having a rectangular plan configuration and sized to support a crew of workmen overlies the frame 15. Preferably, the platform 20 measures about 8 feet in width by about 12 feet in length and is constructed so as to be rigid both lengthwise and widthwise.

In order to raise and lower the platform 20 with respect to the frame 15, a linkage and actuator system is provided. As best seen in FIG. 2, the linkage system comprises an elongated boom assembly 22 pivotally connected at R, to the front of the platform 20, a compression member assembly 23 pivotally connected at P to the boom assembly 22 and pivotally connected at P to the frame 15, and a tension member assembly 24 pivotally connected at P to the other or rear end of the boom assembly 22 and pivotally connected at P to the frame 15. A first or main hydraulic actuator 25 connected the compression member assembly 23 to the rear of the frame 15, and upon extension and retraction, the actuator 25 pivots the compression member assembly 23 counterclockwise and clockwise, respectively. As will be discussed more fully hereinafter, second or auxiliary hydraulic actuator means comprising a pair of actuators 27a and 27b interconnects the platform 20 and the boom assembly 22 for levelling the platform 20 during raising and lowering thereof.

With this structure, extension of the main actuator 25 pivots the compression member assembly 23 counterclockwise, and by virtue of the interconnection of the tension member assembly 24 between the frame and the rear end of the boom assembly 22, the rear end of the boom assembly 22 pivots downwardly about the pivot point P at the outer end of the compression member assembly. This causes the front end of the boom assembly 22 to move upwardly for raising the platform 20. Of course, retraction of the actuator 25 causes the reverse to occur for lowering the platform 20.

For the purpose of ensuring substantially vertical movement of the platform with a minimum of horizontal front to rear displacement during raising and lowering, it is important for certain dimensional relations to be observed in the design of the linkage system. For example, as may be seen in FIG. 2, the dimension between the pivot points P and P of the tension member assembly 24 is less than the corresponding dimension between the pivot points P and P of the compression member assembly 23. Moreover, the dimension between the pivot points P and P is greater than both of the aforementioned dimensions. In the present invention, it has been found desirable for the secondmentioned dimension (Pg-P to be related to the firstmentioned dimension (P -P in a ratio of about l.3/l and for the third-mentioned dimension (P -P to be related to the first-mentioned dimension in a ratio of about 1.7/1. The dimension between the pivot point P and the pivot point P is related to the (P -P dimen sion in a ratio of about /2The dimension between pivot points P P, is related to the dimension between the pivot points P and P, in a ratio of about 1/6. A preferred value for the P,P,-, dimension is about 84 inches; a preferred value for the P -P dimension is about lO8 inches; a preferred value for the P -l dimension is about 152 inches; a preferred value for the P3'P3 dimension is about 46 inches; and a preferred value for the P -P dimension is about 120 inches. The above ratios are determined when the compression member assembly is disposed horizontally and the tension member assembly is disposed at about a 5 downward angle with respect to horizontal and the boom is disposed at about a 6 upward angle with respect to horizontal as for example when the apparatus is in its folded transport configuration.

As may be seen in FIGS. 1 and 2, the compression and tension member assemblies 23 and 24, respectively, extend away from the frame 15 in substantially parallel relation, and the compression member assembly 23 is pivoted from its lower limit position adjacent the frame 15 and into its upper limit position at a substantially right angle to the frame 15. For this purpose, the main actuator has a casing 25a which is pivotally connected at P to the rear of the frame 15, and the actuator 25 has an operating rod 25b which is pivotally connected at P to the compression member assembly 23. In the illustrated embodiment, the main actuator pivot point P is located below the level of the compression member pivot point P and the operating rod pivot point P is located outwardly adjacent the compression member to frame pivot point P The pivot point P of the tension member assembly 24 is located intermedi ate the compression member to frame pivot point P and the main actuator to frame pivot point P., The line of action of the actuator 25 is thereby inclined and directed above the compression member pivot point P,, a sufficient distance as to provide an adequate moment arm to initiate pivoting of the compression member assembly 23 even when in its downwardmost or transportation position with the rod 25b fully retracted. Of course, when the rod 25b is fully extended, the platform 20 is in its uppermost limit position. In the present invention, the length of the stroke of the actuator rod 25b is selected to be about 36 inches, or approximately A of the P -P dimension.

For the purpose of providing a rigid but relatively lightweight apparatus, the various components of the linkage system are arranged in pairs and are fabricated of hollow structural members. For instance, as best seen in FIG. 3, the boom assembly 22 comprises a pair of boom members 22a and 22b which are disposed in spaced parallel relation and tied together at spaced locations by transverse braces 31, 32 and 33. The compression member assembly 23 similarly comprises a pair of compression members 23a and 23b. Each member, such as the left hand member 230, mounts onto its associated frame member 15a between a pair of plates 34a and 34b welded on opposite sides of the frame member 15a. In the illustrated embodiment, the boom members 220 and 22b are located inboard of the compression members 230 and 23b, and the pivot connection P is provided by a shaft 35 which extends through the pairs of members within bushings. The tension member assembly 24 also comprises a pair of members 24a and 24b, and these members are located inboard of the boom members 22a and 22b. The tension members 24a and 24b are secured to the boom members 22a and 22b in the same manner in which the compression members 23a and 23b are secured.

The lower end of each tension member, such as the left hand member 240, is pivotally connected by a pin 29 between a pair of plates 36a and 36b which project upwardly from a supplemental frame member 150. The right hand tension member 24b is similarly connected to a right hand supplemental frame member 15d. The supplemental frame members and 15d are located inboard of the main frame members 150 and 15b and are fastened to the front brace 16. The supplemental frame members are secured to the rear brace 17 by a depending block 39 to which the casing 250 of the main hydraulic actuator 25 is fastened. Thus, the pivot connection P of the lower end of each tension member 24a and 24b is located at a level intermediate the level of the pivot connections P and P of the compression members and actuator, respectively. By virtue of this structure, the apparatus 10 may be folded into a relatively compact transportation configuration.

The platform 20 is leveled automatically as the linkage system moves. To this end, the auxiliary hydraulic actuators 27a and 27b are mounted outboard of the boom members 22a and 22b on arms 41a and 41b extending laterally of the boom members. Each actuator, such as the left actuator 270 (FIG. 3) has an operating rod 270 which is pivotally fastened to the platform 20 by a pin 43 extending through a pair of depending plates 44a and 44b. Moreover, the head ends of the easings are pivotally mounted in yokes 45a and 45b, to permit the casings 27a and 27b to pivot relative to their mounting arms and thence relative to the boom 22 during extension and retration. Thus, extension and retraction of the auxiliary actuators 27a and 27b causes the platform 20 to pivot relative to the boom assembly 22 about the pivot point P In order automatically to extend and retract the actuators 27a and 27b, an hydraulic control system is provided. As best seen in FIG. 6 (Sheet 3) the system includes a four-way, hydraulically-actuated, closedeenter slave valve 50 connected to opposite ends of each actuator, such as the actuator 27a. The slave valve 50 is internally constructed so that pressurized control fluid applid at controller 50a causes extension of the rod 270, and pressurized control fluid at the right controller 50b causes retraction of the rod 27c. The slave valve 50 is biased into a closed position to maintain the actuator rod stationary in the absence of control pressure fluid at either controller. Preferably, both actuators 27a and 27b and the main actuator 25 are provided with safety lock valves to prevent collapse of the linkage and hence the platform 20 in the event of a sudden loss in pressure as by breakage of a hydraulic line, etc.

The level of the platform 20 is sensed by a rotary pilot valve or operator 55 which is mounted on the platform 20 adjacent the platform-boom pivot connection P,. The valve 55 is conventional, having a housing 56, a rotor 57, and a mass 58 depending from a shaft 59 connected to the rotor 57. The rotor 57 has passages 57a, 57b and 57c which control the distribution of pressure fluid to the slave valve 50, depending on the orientation of the rotor 57 with respect to the housing 56. The rotor shaft 59 is disposed with its pivot axis parallel to the pivot axis P, of the platform 20. The housing 56 is immersed in hydraulic fluid 60 contained in the body of the valve 55, the fluid 60 serving to dampen movement of the mass 58.

Hydraulic fluid is supplied to pressure ports 65 and 66 of the valve housing 56 by a supply line 67 connected through a pump 68 to a sump 69. Control pressure fluid is supplied to controller 50a by a line 71 and is supplied'to controller 50b by a line 72. The line 71 is connected to control port 74, and the line 72 is connected to the control port 75. A return line 70 is provided to vent control fluid from the valve 55 and to the sump 69.

With this system, clockwise pivotal movement of the housing 56 relative to the rotor 57, as during clockwise pivotal movement of the boom 22 during raising of the platform, causes the rotor passage 57a to provide fluid communication from pressure port 66 to pressure port 74 and through line 71 to controller 50a of the slave valve 50 for extending the rod 27c of the actuator 27a to pivot the platform 20. At the same time, control fluid from controller 50b is vented to the sump 69 by virtue of the registry of the rotor passage 57b with pressure ports 76 and 75 and hence lines 70 and 72. Of course, during lowering of the platform 20, the rotor passage 57c provides fluid communication between ports 65 and 75 so that control fluid is flowed through line 72 to controller 50b from pressure, and control fluid is vented through the line 70 to the sump 69 by virtue of the registry provided by the passage 57b with ports 76 and 74 and hence lines 70 and 71. Thus, with this control system, the platform 20 is maintained substantially level during raising and lowering thereof, and the level control is automatic.

If desired, the structure of the present invention may be modified to enable a single auxiliary actuator to level the platform. As best seen in FIGS. 4 and 5, an hydraulic actuator 127 is mounted in a yoke which is secured to a brace 131 extending between boom members 1220 and l22b. The actuator 127 has an operating rod l27c which is pivotally connected to a crank 170. The crank extends upwardly from a shaft 171 which extends between and is rotatably mounted to boom members 122a and 122b. A pair of arms 172a and l72b extend away from the crank-shaft 171, and each arm such as the arm 172a is pivotally connected to a link 1730 which in turn is pivotally connected to the underside of the platform 120. Thus, extension of the actuator rod 1270 pivots the crank 170 and arms 172a and 172k clockwise (FIG. 4) to displace the links 173a and l73b lengthwise for pivoting the platform 120 counterclockwise relative to the end of the boom members 1220 and l22b. Actuator of the single actuator 127 may be controlled automatically by the system illustrated in FIG. 6 to maintain the platform 120 level during raising and lowering thereof. With this structure, a single relatively short stroke-actuator may be utilized in lieu of the two relatively long stroke (and expensive) actuators described in the first mentioned embodiment.

In view of the foregoing, it should be apparent that novel man-lifting apparatus has now been provided. The apparatus is strong and safe while being relatively simple in construction.

While preferred embodiments of the present invention have been described in detail, various modifications, alterations and changes may be made without departing from the spirit and scope of the present invention as defined in the appended claims.

I claim:

1. Load lifting apparatus, comprising:

a frame,

a compression member pivotally connected to said frame at one location,

an elongated boom pivotally connected to said compression member,

an elongated load support platform pivotally connected to one end of said boom and extending therefrom so as to overlie said boom and said frame for supporting a load moveable on the platform above the frame,

a rigid tension member pivotally connected to the other end of said boom and pivotally connected to said frame at another location spaced from said one location,

first actuator means connecting said compression member to said frame for pivoting the compression member and causing said tension member to pivot said boom relative to the compression member for raising and lowering said load support, and

second actuator means associated with said support and boom for pivoting said support relative to said boom to permit leveling of said support during raising and lowering thereof, whereby said load support platform may be raised and lowered upon extension and retraction of said first actuator means.

2. Apparatus according to claim 1 wherein the pivot connection of said tension member to said frame is spaced from the pivot connection of said tension member to said boom 21 first predetermined dimension, the compression member to frame pivot connection is spaced from the compression member to boom pivot connection a second predetermined dimension greater than said first dimension; and the pivot connection of said tension member to said boom is spaced from the pivot connection of said compression member to said frame a third predetermined dimension greater than said second-mentioned dimension.

3. Apparatus according to claim 2 wherein said second dimension is related to said first dimension in a ratio of substantially 1.3/1, and said third dimension is related to said first dimension in a ratio of about 1.7! 1, said ratios being determined when the compression member is disposed horizontally and said tension member is disposed at about a downward angle with respect to horizontal and said boom is disposed at about a 6 upward angle with respect to horizontal.

4. Apparatus according to claim I wherein said members are disposed in substantially parallel relation and said one end of said boom overlies the pivot connection of said compression member to said frame.

5. Apparatus according to claim 4 wherein said first actuator is pivotally connected to said frame at a third location spaced from said first-mentioned frame location and said tension member to frame pivot connection is located intermediate said first and third frame locations.

6. Apparatus according to claim 5 wherein said first actuator is pivotally connected to said compression member outward of said compression member to frame pivot connection, and said first actuator is inclined with respect to said frame to dispose the line of action of the first actuator transverse to the compression and tension members and in the same direction as the boom.

7. Apparatus according to claim 6 including a vehicle having a pair of spaced parallel chassis members, said frame including a pair of main frame members fastened to said chassis members and at least one supplemental frame member inclined with respect to said main members and disposed inboard of said chassis members, said tension member being secured to said supplemental frame member at a level below the level of said compression member to frame pivot connection, to afford folding of the apparatus into a compact transport configuration.

8. Apparatus according to claim 1 including automatic leveling means associated with said second actuator means for maintaining said support level during raising and lowering thereof, said automatic leveling means including an operator mounted to said support, gravity sensing means associated with said operator, and means connecting said operator means to said second actuator means, said operator being operable to extend and retract said second actuator means to maintain said support level as said boom pivots in opposite directions relative to said compression member.

9. Apparatus according to claim 8 wherein said operator means includes a housing and a rotor mounted for rotation relative to said housing about a horizontal axis parallel to the pivot axis of the support, and said gravity sensing means includes a mass connected to said rotor and depending below its pivot axis for causing said rotor to pivot relative to said housing during pivotal movement of said boom.

10. Apparatus according to claim 9 wherein said second actuator means includes at least one hydraulic cylinder, and said operator includes rotary valving means associated with said rotor in said housing, said connecting means providing fluid communication to opposite ends of said cylinder for supplying pressure fluid thereto and exhausting pressure fluid therefrom for extending and retracting said cylinder in response to pivotal movement of said housing relative to said rotor and said valving means.

ll. Apparatus according to claim 10 wherein said connecting means includes slave valve means associated with said rotary valving means and connected to said second actuator means and a source of pressure fluid to extend and retract said second actuator means in response to operation of said rotary valving means.

12. Apparatus according to claim 1 wherein said support is elongated and overlies said boom, and said second actuator means includes a pair of hydraulic cylinders, means pivotally mounting said cylinders outboard of said boom, and means pivotally connecting said cylinders to said support.

13. Apparatus according to claim 1 wherein said second actuator means includes an hydraulic cylinder, a shaft pivotally connected to said boom adjacent said support pivot connection, a crank arm connected to said shaft, at least one arm secured to said shaft, and at least one link connecting said arm to said support for pivoting the support relative to the boom upon extension and retraction of said hydraulic cylinder.

14. Apparatus according to claim 1 wherein said second actuator means includes an hydraulic cylinder, a crank having a shaft pivotally connected to said boom adjacent said support pivot connection, at least one arm secured to said shaft and connected to said cylinder, and at least one link connecting said arm to said support for pivoting the support relative to the boom upon extension and retraction of said hydraulic cylinder.

Patent No.

Inventor(s) July 8. 1275 Robert A. Beucher It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column Column Column [SEAL] Signed and Sealed this thirtieth D a); 9f March 1 9 76 Arrest" C. MARSHALL DANN Commissioner of Parents and Trademarks RUTH C. MASON Arresting Officer 

1. Load lifting apparatus, comprising: a frame, a compression member pivotally connected to said frame at one location, an elongated boom pivotally connected to said compression member, an elongated load support platform pivotally connected to one end of said boom and extending therefrom so as to overlie said boom and said frame for supporting a load moveable on the platform above the frame, a rigid tension member pivotally connected to the other end of said boom and pivotally connected to said frame at another location spaced from said one location, first actuator means connecting said compression member to said frame for pivoting the compression member and causing said tension member to pivot said boom relative to the compression member for raising and lowering said load support, and second actuator means associated with said support and boom for pivoting said support relative to said boom to permit leveling of said support during raising and lowering thereof, whereby said load support platform may be raised and lowered upon extension and retraction of said first actuator means.
 2. Apparatus according to claim 1 wherein the pivot connection of said tension member to said frame is spaced from the pivot connection of said tension member to said boom a first predetermined dimension, the compression member to frame pivot connection is spaced from the compression member to boom pivot connection a second predetermined dimension greater than said first dimension; and the pivot connection of said tension member to said boom is spaced from the pivot connection of said compression member to said frame a third predetermined dimension greater than said second-mentioned dimension.
 3. Apparatus according to claim 2 wherein said second dimension is related to said first dimension in a ratio of substantially 1.3/1, and said third dimension is related to said first dimension in a ratio of about 1.7/1, said ratios being determined when the compression member is disposed horizontally and said tension member is disposed at about a 5* downward angle with respect to horizontal and said boom is disposed at about a 6* upward angle with respect to horizontal.
 4. Apparatus according to claim 1 wherein said members are disposed in substantially parallel relation and said one end of said boom overlies the pivot connection of said compression member to said frame.
 5. Apparatus aCcording to claim 4 wherein said first actuator is pivotally connected to said frame at a third location spaced from said first-mentioned frame location and said tension member to frame pivot connection is located intermediate said first and third frame locations.
 6. Apparatus according to claim 5 wherein said first actuator is pivotally connected to said compression member outward of said compression member to frame pivot connection, and said first actuator is inclined with respect to said frame to dispose the line of action of the first actuator transverse to the compression and tension members and in the same direction as the boom.
 7. Apparatus according to claim 6 including a vehicle having a pair of spaced parallel chassis members, said frame including a pair of main frame members fastened to said chassis members and at least one supplemental frame member inclined with respect to said main members and disposed inboard of said chassis members, said tension member being secured to said supplemental frame member at a level below the level of said compression member to frame pivot connection, to afford folding of the apparatus into a compact transport configuration.
 8. Apparatus according to claim 1 including automatic leveling means associated with said second actuator means for maintaining said support level during raising and lowering thereof, said automatic leveling means including an operator mounted to said support, gravity sensing means associated with said operator, and means connecting said operator means to said second actuator means, said operator being operable to extend and retract said second actuator means to maintain said support level as said boom pivots in opposite directions relative to said compression member.
 9. Apparatus according to claim 8 wherein said operator means includes a housing and a rotor mounted for rotation relative to said housing about a horizontal axis parallel to the pivot axis of the support, and said gravity sensing means includes a mass connected to said rotor and depending below its pivot axis for causing said rotor to pivot relative to said housing during pivotal movement of said boom.
 10. Apparatus according to claim 9 wherein said second actuator means includes at least one hydraulic cylinder, and said operator includes rotary valving means associated with said rotor in said housing, said connecting means providing fluid communication to opposite ends of said cylinder for supplying pressure fluid thereto and exhausting pressure fluid therefrom for extending and retracting said cylinder in response to pivotal movement of said housing relative to said rotor and said valving means.
 11. Apparatus according to claim 10 wherein said connecting means includes slave valve means associated with said rotary valving means and connected to said second actuator means and a source of pressure fluid to extend and retract said second actuator means in response to operation of said rotary valving means.
 12. Apparatus according to claim 1 wherein said support is elongated and overlies said boom, and said second actuator means includes a pair of hydraulic cylinders, means pivotally mounting said cylinders outboard of said boom, and means pivotally connecting said cylinders to said support.
 13. Apparatus according to claim 1 wherein said second actuator means includes an hydraulic cylinder, a shaft pivotally connected to said boom adjacent said support pivot connection, a crank arm connected to said shaft, at least one arm secured to said shaft, and at least one link connecting said arm to said support for pivoting the support relative to the boom upon extension and retraction of said hydraulic cylinder.
 14. Apparatus according to claim 1 wherein said second actuator means includes an hydraulic cylinder, a crank having a shaft pivotally connected to said boom adjacent said support pivot connection, at least one arm secured to said shaft and connected to said cylinder, and at least one link connecting said arm to saId support for pivoting the support relative to the boom upon extension and retraction of said hydraulic cylinder. 